AbstractGreen tea is a worldwide used beverage rich in fluoride and caffeine. To study the effect of excessive green tea intake versus fluoride and caffeine on body weight and serum thyroid hormones in male mice. Also, to confirm the effect of excessive green tea intake on thyroid gland was due to its fluoride and caffeine content or not. Thirty Male albino mice 25-30 gm weight were divided into five groups. Control (C) group (6 mice) receiving distilled water. Green tea (GT) treated group; 6 mice were given a 5 gm% tea hot water extract as their sole water supply. Fluoride (FL) treated group, 6 mice were given fluorine excess solution as their only water supply. Caffeine (Caf) treated group, 6 mice were treated with caffeine (6.25 mg/kg ip). Propylthiouracil (PTU) treated group, 6 mice were treated with PTU (10 mg/kg ip). Each of the five groups is treated with the corresponding substance for 30 days, then sacrificed under ether anesthesia, blood was collected to study serum levels of T3 and T4. There was a significant decrease in serum T3 in PTU treated group (0.72±0.03), GT treated group (0.96±0.04), FL treated group (0.93±0.04) and Caf treated group (1.46±0.08) in comparison to the C group (1.71±0.05).Also, there was a significant decrease in serum T4 in PTU treated group (15.71±1.26), GT treated group (30.07±2.29) and FL treated group (22.03±1.95)in comparison to the C group (51.1±3.15). But, there was an insignificant change in serum T4 in Caf treated group (45.55±2.73) in comparison to the C group (51.1±3.15). Green tea unfractionated aqueous extract decreased serum T3 and T4 and at the same time, increased final total body weight without a significant effect on the relative thyroid weight in comparison to the control group and this may be at least partly due to its content of fluoride and caffeine. Further work should be done on green tea free fluoride and caffeine to confirm this result.